Auto-ignition model based on tabulated detailed kinetics and presumed temperature PDF – Application to internal combustion engine controlled by thermal stratifications

The prediction of the auto-ignition sensitivity to the temperature in new engine combustors is a challenge in the community of numerical combustion. This paper is devoted to the modeling of temperature fluctuations for the simulation of reactive flows in real internal engine configurations. It aims at validating the temperature fluctuation equation model Truffin and Benkenida and its coupling with the ECFM3Z combustion model of Colin and Benkenida. Especially, this study focuses on the auto-ignition process which is described by the TKI (Tabulated Kinetics for Ignition) model of Knop and Jay. TKI is based on a tabulation method for reaction rates and its coupling with the temperature fluctuation is achieved through a presumed PDF approach. The integral limits for the PDF integration are determined locally through transport equations with appropriate closures on isothermal walls. The resulting model, called TKI–υ_T, is applied on Homogeneous Charge Compression Ignition (HCCI) combustion mode engine for which the only source of thermal stratification is wall heat loss. Comparisons with experiments demonstrate the impact of temperature fluctuations and the ability of the model to improve the prediction of the auto-ignition model.     

A temperature fluctuation equation model dedicated to the computation of turbulent thermal layers in high Reynolds internal flows

The paper deals with the modelling of temperature fluctuations in the fresh gases for the simulation of turbulent internal flows. For this purpose, a transport equation for the sensible enthalpy variance is treated. The proposed dynamic model for the scalar dissipation rate incorporates the effect of the turbulent Reynolds number. The wall closure is based on a non-isothermal formulation and accounts for the non-equilibrium state of the boundary layer. The developed models are implemented into the compressible code IFP-C3D. Results of the computations are successfully compared with experiments and DNS data for a slightly heated jet and moderate non-isothermal walls.     

Characterization of fluorescein isothiocyanate-dextrans used in vesicle permeability studies

Fluorescein Isothiocyanate-dextrans of various weight average molecular masses (4,400-487,000) were analyzed in buffer solution for pH, osmolarity, fluorescence intensity as a function of the polymer concentration, average molecular masses, and radii of gyration. Labeling of polymers and conformation of the polymers were characterized by high-performance gel exclusion chromatography (HPLC-GEC) and small-angle X-ray scattering. The fluorescence measurements evidence the absence of fluorescence quenching of the FITC chromophores but the existence of an inner filter effect at high polymer concentration. The conformation of the polymers in buffer is very likely of random coil type, as shown by the relationship between the radii of gyration and the weight-average molecular masses of the dextrans (Mw). The medium used to analyze the FITC-dextrans by HPLC-GEC strongly influences their elution behavior. In buffer medium, they are sieved over the TSK G4000 PW column through a single population according to their Mw. whereas in pure water, they are separated into several species by an exclusion mechanism that depends on the number of labeled sites per dextran molecule. A Monte Carlo simulation was used to analyze the distribution of the fluorescent labels. HPLC-GEC in water could interestingly be applied to yield labeled polymers bearing a known number of functionalized groups.     

Modular mutagenesis of a TEM-barrel enzyme: the crystal structure of a chimeric E.coli TIM having the eighth {beta}{alpha}-unit replaced by the equivalent unit of chicken TIM

Abstract The crystal structure of a hybrid Escherichia coli triosephosphateisomerase (TIM) has been determined at 2.8 Å resolution.The hybrid TIM (ETIM8CHI) was constructed by replacing the eighthß-unit of E.coli TIM with the equivalent unit of chickenTIM. This replacement involves 10 sequence changes. One of thechanges concerns the mutation of a buried alanine (Ala232 instrand 8) into a phenylalanine. The ETIM8CHI structure showsthat the A232F sequence change can be incorporated by a side-chainrotation of Phe224 (in helix 7). No cavities or strained dihedralsare observed in ETIM8CHI in the region near position 232, whichis in agreement with the observation that ETIM8CHI and E.coliTIM have similar stabilities. The largest CA (C-alpha atom)movements, 3 Å, are seen for the C-terminal end of helix8 (associated with the outward rotation of Phe224) and for theresidues in the loop after helix 1 (associated with sequencechanges in helix 8). From the structure it is not clear whythe k_cat of ETIM8CHI is 10 times lower than in wild type E.coliTIM     

évaluation économique de la thérapie cognitivo-comportementale des troubles anxieux.

This literature review examines the results of cost-effectiveness studies of cognitive-behaviour therapies published up to June 2003. Cost offsets likely to be derived from effective treatment of anxiety problems are also examined. A summary of results suggests the following: 1) cognitive-behaviour therapy is cost-effective compared to drug therapy for the treatment of panic disorder and social phobia; 2) group treatments and short courses as well as new technologies are promising alternatives to conventional therapy; 3) the existence of cost offsets for anxiety disorders has yet to be ascertained. Research approaches are suggested to cover significant shortcomings in the methodologies of studies conducted to date. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reasoning about geological space: Coupling 3D GeoModels and topological queries as an aid to spatial data selection

Topological relationships between geological objects are of great interest for mining and petroleum exploration. Indeed, adjacency, inclusion and intersection are common relationships between geological objects such as faults, geological units, fractures, mineralized zones and reservoirs. However, in the context of 3D modeling, actual geometric data models used to store those objects are not designed to manage explicit topological relationships. For example, with Gocad^© software, topological analyses are possible but they require a series of successive manipulations and are time consuming. This paper presents the development of a 3D topological query prototype, TQuery, compatible with Gocad^© modeling platform. It allows the user to export Gocad^© objects to a data storage model that regularizes the topological relationships between objects. The development of TQuery was oriented towards the use of volumetric objects that are composed of tetrahedrons. Exported data are then retrieved and used for 3D topological and spatial queries. One of the advantages of TQuery is that different types of objects can be queried at the same time without restricting the operations to voxel regions. TQuery allows the user to analyze data more quickly and efficiently and does not require a 3D modeling specialist to use it, which is particularly attractive in the context of a decision-making aid. The prototype was tested on a 3D GeoModel of a continental red-bed copper deposit in the Silurian Robitaille Formation (Transfiguration property, Québec, Canada).     

Bitterness and astringency of flavan‐3‐ol monomers,dimers and trimers

Intensity of astringency and bitterness of seven flavonoid compounds was evaluated by a time‐intensity (TI) procedure. Eighteen trained judges rated intensity continuously from ingestion, through expectoration at 10 s until extinction of the sensation. The seven stimuli included two flavan‐3‐ol monomers, (+)‐catechin and (−)‐epicatechin, three dimers and two trimers synthesised from catechin or epicatechin by condensation with (+)‐dihydroquercitin. As the degree of polymerisation increased, maximum bitterness intensity (I_max) and total duration (T_tot) decreased whereas astringency I_max increased. The monomers were significantly higher in bitterness at I_max than the dimers, which were significantly higher than the trimers. Astringency I_max of the monomers was lower than the dimers or trimers, although no significant difference was found in T_tot among the polymer classes. The bond linking the monomeric units had an influence on both sensory properties. The catechin‐catechin dimer linked by a 4→6 bond was more bitter than both catechin‐(4→8)‐catechin and catechin‐(4→8)‐epicatechin. Astringency was affected by both the specific linkage and the identity of the monomeric units with the dimer, catechin‐(4→8)‐catechin, being lower in astringency than either catechin‐(4→6)‐catechin or catechin‐(4→8)‐epicatechin. © 1999 Society of Chemical Industry     

Surfactant‐Stabilized Aqueous Iridium(0) Colloidal Suspension: An Efficient Reusable Catalyst for Hydrogenation of Arenes in Biphasic Media

Aqueous suspensions of iridium nanoparticles produced by the chemical reduction of IrCl₃ assisted by sonication, in the presence of N,N‐dimethyl‐N‐cetyl‐N‐(2‐hydroxyethyl)ammonium chloride salt as surfactant, have shown an efficient activity for the catalytic hydrogenation of various aromatic derivatives in biphasic media under mild conditions. These nanocatalysts can be reused for further runs with a total conservation of activity and provided significant catalytic lifetime for anisole hydrogenation in pure water with 3000 total turn‐over (TTO).     

Nanoscale coordination polymers exhibiting luminescence properties and NMR relaxivity

This article presents the first example of ultra-small (3-4 nm) magneto-luminescent cyano-bridged coordination polymer nanoparticles Ln0.33(3+)Gdx3+/[Mo(CN)8]3- (Ln=Eu (x=0.34), Tb (x=0.35)) enwrapped by a natural biocompatible polymer chitosan. The aqueous colloidal solutions of these nanoparticles present a luminescence characteristic of the corresponding lanthanides (5D0→7F0-4 (Eu3+) or the 5D4→7F6-2 (Tb3+)) under UV excitation and a green luminescence of the chitosan shell under excitation in the visible region. Magnetic Resonance Imaging (MRI) efficiency, i.e. the nuclear relaxivity, measurements performed for Ln0.33(3+)Gdx3+/[Mo(CN)8]3- nanoparticles show r1p and r2p relaxivities slightly higher than or comparable to the ones of the commercial paramagnetic compounds Gd-DTPA? or Omniscan? indicating that our samples may potentially be considered as a positive contrast agent for MRI. The in vitro studies performed on these nanoparticles show that they maybe internalized into human cancer and normal cells and well detected by fluorescence at the single cell level. They present high stability even at low pH and lack of cytotoxicity both in human cancer and normal cells.